Taiwan patent publication No. 568160 disclosed that a “structure of fireproof doors” is relevant to a fire door lock. Two latch bolts are disposed at an upper end and a lower end of a fire door separately, and the latch bolts can be blocked by two stoppers disposed at a door frame therefore forming a locked state. Usually, the blocked latch bolts departs from the stoppers and leads to an unlocked state via the actuation of a main lock. With reference to FIG. 1, a fire door lock comprises a stopper 20 disposed at a door frame 10 and a latch 40 disposed at a fire door 30. A latch bolt 41 of the latch 40 can be blocked by the stopper 20 to prevent the fire door 30 from being opened therefore possessing burglarproof and fireproof functions. With reference to FIG. 2, the latch bolt 41 disposed at the fire door 30 merely blocks the stopper 20 disposed at the door frame 10, once a fire occurred, the fire would burn and deform the door frame 10 or the fire door 30. Accordingly, the stopper 20 cannot block the latch bolt 41 of the latch 40 disposed at deformed fire door 30. Therefore, the fireproof function of the fire door 30 would be all lost.